Dr. Drummond on the Equivocal Generation of Entozoa. 101 



the motions of the animal are in the highest degree slow and 

 sluggish, which I have likewise observed in Cyathina, Oculina 

 and Cladocora. 



Plate IV. Fig. G. Desmophyllum Stellaria, Ehrenberg. Nat. size, sitting 

 on Nullipora Lithophyllurn expansum, Phil. 



XV. — Thoughts on the Equivocal Generation of Entozoa. By 

 Jas. L. Drummond, M.D., Professor of Anatomy and 

 Physiology in the Royal Belfast Institution, &c. 



In studying the Entozoa, one of the first things which de- 

 mands our attention, is the peculiarity of the situations which 

 they occupy. When we look abroad upon the features of the 

 globe which we inhabit, we find that every part is filled with 

 animal and vegetable life ; whether we visit the frozen regions 

 of the poles, or the countries for ever exposed to the heat of an 

 equatorial sun, we see that every clime has its animals and 

 plants, and these in general, so constituted in their structure 

 and ceconomy, as to be fitted peculiarly for the circumstances 

 of the place in which they reside. The White Bear delights 

 in the perennial snows and ice of its native region, and the 

 Lion in the fervour of the torrid zone ; but were they to change 

 situations, the former would die from the excessive heat, and 

 the latter would as certainly perish from the intolerable cold. 



And so it is with the Entozoa ; they have been ordained 

 to inhabit, alone, the interior of other animals ; and though 

 many of them will live for several days when removed from 

 that situation and put in water, yet that can only be deemed 

 a lingering death, for at length they infallibly perish from the 

 unnatural circumstances in which they are placed. It has 

 been asserted, indeed, that some of the intestinal worms 

 have been found living in other situations. Thus, Linnaeus 

 supposed that the Fluke-worm (Distoma hepaticum) was to 

 be found in fresh water, as also the common Tape-worm in 

 muddy pools, and the Ascaris vermicular is in marshes among 

 the roots of decaying plants. (Rudolphi, i. 371.) But it has 

 been shown by Muller and Rudolphi, that he had mistaken 

 other external species of animals for true Entozoa ; that his 

 supposed Taenia and Fluke-worm were the Planaria lactea, 

 and his Ascaris vermicularis a quite different animal. 



But even admitting that a true entozoon should be found in 

 a pool or rivulet of fresh water, still* something more would be 

 necessary to prove that such was its natural habitat. Every 

 one knows that when an animal is infested with Tape-worm, 

 portions of the latter are frequently ejected along with the 



